An Innovative Approach to Water Storage at a Sustainable Tanzanian Home
Just outside of Arusha, Tanzania, is ‘Kesho Leo’– a sustainable home for vulnerable women and children operated by FoodWaterShelter. The principles of permaculture underpin the daily lives of the Kesho Leo residents. It is currently the home of seven families, each headed by a Tanzanian mama who cares for up to five children, including orphans. In addition to the daily essentials, Kesho Leo provides the many other aspects that a ‘home’ needs; access to family and social support, access to education and health, and very importantly – access to community.
Permaculture meeting the needs of the Kesho Leo residents
Revolving around the community and education aspects of Kesho Leo are the permaculture systems that strive to provide all of the food, water and energy needs of the residents. Basic needs of water, sanitation and power are provided through rainwater harvesting, innovative batch compost toilet systems, and solar power.
The Tanzanian residents, staff and Western volunteers of FoodWaterShelter operate three separate farms, each with an individual aim and each under different stages of development. One farm manages the utilisation of grey water and humanure in a food forest and chicken run arrangement still under development. A second farm, still undergoing permaculture development and detached from Kesho Leo, produces organic vegetables sold for profit in Arusha.
Surface water management and the use of swales are
integral to the Kesho Leo farms
The third farm, and the most developed, is an example of how locally appropriate solutions (suitable for use by subsistence farmers) can be integrated to create an intensive system that manages water, nutrients and soil. This farm, less than half a hectare in size (and that includes a playground) includes traditional shelters for livestock such as goats, cows and pigs, from which the manure is collected and directed into a biodigester for the production of methane gas for cooking.
The slurry from the biodigester then serves a couple of purposes as it gravity feeds through a series of swales between the organic garden beds (each the same size to allow the use of a mobile chicken tractor) and into our fish and duck ponds where the nutrient rich water promotes the growth of phytoplankton and algae to feed tilapia. These ponds are the final stages in preventing many of the normal farm losses and allows nutrients, soil and water to be recaptured and returned to where they’re needed.
Not only does this farm manage water, nutrients and soil in a cyclic system, but it provides a variety of produce for the Kesho Leo residents as well as educational opportunities for the nearby community and visitors.
Organic garden beds, compost, swales and fish ponds are just some of
the components of the integrated system that manages nutrients, soil and water
to meet the needs of the Kesho Leo residents.
In developing Kesho Leo, FoodWaterShelter has worked to select locally appropriate techniques and solutions that are already available in the local area, and then fit them into an integrated system. However, FoodWaterShelter also uses Kesho Leo as a demonstration and experimental site for some less mainstream, but no less appropriate solutions. One of these was the development of an underground water storage system constructed out of tyres. More accurately, this system is an ‘aquifer’ where old tyres are stacked to partially fill the void space and to provide support that has allowed the top of the aquifer to be soiled and grassed for a children’s playground.
The process for construction is relatively simple.
1. Select a site where you know the soils will hold water, and where you also will be able to manage the delivered water, particularly so that sedimentation can be reduced.
2. Dig the void as you would with a dam, including battered sides.
The aquifer void and the first row of tyres being laid
3. Using old car or truck tyres, stack them neatly in columns with the aim of finishing with a flat surface approximately three tyre thicknesses below the proposed finished surface. To provide extra support, it is worthwhile filling every third tyre column with rocks or large stones to create stronger support columns that will later hold up the playground.
The tyres are neatly stacked, and the stone support columns are formed
4. At this point, the next step will depend on if you used larger truck tyres, or smaller car tyres. If car tyres, you can probably move straight onto the next stage. But if you used larger truck tyres, you may find that the gaps in and between the tyres are too large to bridge with rocks. Hence, at Kesho Leo we had to use a layer of weld mesh (similar, but smaller than concrete reinforcing mesh) that supported the rocks added subsequently.
At a depth approximately three tyres below the desired finished surface,
a layer of weld mesh or similar material may be required to support rocks from
falling into the gaps between tyres.
5. Then place a layer of permeable geo-fabric across the top of the tyres that will allow water to pass through, but not soil. This geo-fabric should be well supported by the level surface of the tyre columns (or the weld mesh). At Kesho Leo, old cement bags were sewn together to create the geo-fabric.
6. The second last row of tyres is then placed in a grid arrangement, as neatly as possible . This row is then completely filled with rocks or large stones with the aim of having a flat surface, approximately two tyre thicknesses below the finished level.
A layer of ‘geofabric’ (possibly made from sewing cement bags together)
is placed before the second last row of tyres is filled with rocks.
7. Place another layer of geofabric (or cement bags).
8. Place another layer of tyres, and this time back fill it with soil.
9. Finally, cover the top of the aquifer with 200 to 300 mm of topsoil and grass it for a playground.
The final row of tyres is filled with topsoil, with a final covering
of 200 to 300 mm to allow for grass to establish.
10. During the construction process you will need to have considered inlets and outlets for your irrigation water. At Kesho Leo, the overflow from the rainwater tanks flows into the aquifer. At your site, you may have access to a temporary irrigation system that you may be able to collect water from for later use, or a carpark where relatively clean water runs off. Just be careful that water you are directing into the aquifer is not too rich in sediment or you may need a sedimentation trap. To extract the water, Kesho Leo’s aquifer simply has one column that extends all the way to the surface and remains open to act as a shallow well from which a pump can be used to extract the water.
The completed aquifer, with only two concrete covers
visible above the inlet and outlet
This concept of an artificial aquifer is not uncommon around the world and you can find similar systems under public car parks, sports fields and golf courses. Generally though, they use specially designed and bought structural items — not reused tyres and cement bags.
So why go to all this effort? What are the advantages?
- The tyre aquifer saves space. An open dam and water storage means that you can’t do anything with the land above it. The Kesho Leo aquifer allows a play area for children above. The next stage is to experiment with the growing of vegetables on top;
- There’s reduced evaporation due to the closed top;
- The reduced possibility for mosquito breeding, or at least a system where it can be controlled;
- Improved safety by preventing access to children; and
- The reuse of tyres and old cement bags.
And the disadvantages?
- Unfortunately, the aquifer does mean that the water cannot be used for your fish and ducks; and
- Extracting the water will need a simple pump.
Some of the bounty from the Kesho Leo farm
Despite the fact that it can store around 100,000 litres of irrigation water, Kesho Leo’s aquifer — the first tyre aquifer constructed here — hasn’t been a 100% success. The structural aspects of the aquifer have worked beautifully, but unfortunately the soils engineering wasn’t as successful. As the location selected at Kesho Leo was in soils known to be highly permeable, heavy clay soil was imported and compacted into the aquifer to a total thickness of 300 mm. Unfortunately the aquifer still appears to be leaking quicker than desired, although it is hoped that a good wet season and a sustained soaking of the clays will cause them to expand and seal effectively. At the very least, the Kesho Leo aquifer does operate as a detention basin that captures excess runoff and allows the water to slowly enter the soil profile as it flows downhill beneath a food forest.
Overall, the Kesho Leo aquifer has structurally proven a success. Having now been grassed, the greatest test was around 30 people standing on top and bouncing in time. A slight spring could be felt in the ground, but no movement was obvious; and after 12 months, no subsidence has yet occurred.
For FoodWaterShelter, the next stage is to build a smaller aquifer with garden beds placed over the top. In the right soils and with the right catchment area, the tyre aquifer could prove very successful. Perhaps a small backyard not large enough to allow water storage and gardens simultaneously would be the perfect location. Rain water can be captured off the roof or a small driveway and directed into the aquifer where vegetable gardens are placed on top; taking advantage of vertical space.
If you’d like to learn more about permaculture and appropriate technologies in Tanzania and see the aquifer in action, you may be interested in signing up to the FoodWaterShelter’s Permaculture Design Certificate (PDC) course in June 2012.